The invention is based on a device for measuring the mass of a flowing medium.
A device for measuring the mass of a flowing medium has already been disclosed by EP 0 458 998 B1, which has a measuring element accommodated in a measurement fitting, wherein a flow rectifier and a lattice are accommodated upstream of the measuring element. The flow rectifier is provided in order to generate a flow that is as uniform as possible over the entire inner cross-section of the measurement fitting. To this end, the flow rectifier has a number of flow openings arranged in honeycomb fashion, which are separated from one another by intermediary pieces. The lattice attached to a tube of the flow rectifier that extends in the direction toward the measuring element is intended to produce extremely fine turbulence in the flow in order to produce the most uniform possible flow conditions downstream of the lattice and to produce a stabilization of the measurement signal of the measuring element.
In order to prevent a scattering of the characteristic curve of the measurement signal emitted by the measuring element, it is particularly important to place the lattice in a precise, defined alignment in relation to the flow rectifier.
Even slight variations in the disposition of the lattice in relation to the flow rectifier produces a variation of the characteristic curve of the individual devices produced in a series production. A calibration of the measurement signal is therefore only possible with a corresponding imprecision.
The lattice in EP 0 458 998 B1 is a wire lattice which has individual wires that are woven with one another into a lattice structure. The wire lattice is stamped out of a broad mesh grid in accordance with the opening cross-section of the measurement fitting and is then inserted into the tube of the flow rectifier. When the wire lattice is stamped out of the broad mesh grid, it is impossible to prevent the wires, which are no longer securely fixed after the stamping, from moving until the final fixing in the tube of the flow rectifier, since the wires are only loosely held in the wire fabric after being stamped out of the broad mesh grid. Furthermore, the stamping at least partially eliminates the ability, which exists in the broad mesh grid, of the individual wires to brace each other, which likewise lead to a changed alignment of individual wires within the lattice structure. The wire lattice, whose individual wires that are not securely fixed, is subsequently inserted into the plastic of the tube through the heating of the tube""s plastic material. In this process step as well, a movement of the individual wires in relation to one another cannot be prevented. The individual wires of the lattice structure are therefore not fixed with the required precision in the tube of the flow rectifier so that there is a certain inevitable scattering of the characteristic curve of devices that are produced with a high degree of automation in a series production. As described above, this reduces the measurement precision of the device.
The device according to the invention for measuring the mass of a flowing medium, has the advantage over the prior art that the wires of the wire lattice are fixed with high precision to the tube of the flow rectifier by means of the fixing elements provided. The configuration of the wire lattice is therefore aligned with a high degree of precision in relation to the intermediary pieces of the flow rectifier, wherein a higher reproduction precision can be achieved in a highly automated manufacturing, and consequently, only a slight, practically negligible characteristic curve scattering occurs. The individual flow openings formed between the wires of the wire lattice are therefore aligned with a high degree of precision in relation to the intermediary pieces of the flow rectifier. The function of the wire lattice, namely the production of extremely fine turbulence, is maintained.
Advantageous improvements and updates of the device are possible by means of measures taken.
Advantageously, the wire lattice can be comprised of two independent layers that are not woven together, which is particularly simple from a production engineering standpoint. A first layer of the wire lattice is preferably comprised of a continuous wire and a second layer, likewise comprised of a continuous wire, is placed over the first layer in a different direction, for example orthogonally. The lattice structure is thereby produced directly by means of the fastening of the wires to the tube of the flow rectifier and it is no longer necessary to stamp the wire lattice out of a broad mesh grid.
It is also possible to dispose the wire lattice at a predetermined angle in relation to the intermediary pieces of the flow rectifier. In a particularly advantageous manner, it is possible to vary the mesh width of the wire lattice over the diameter by virtue of the fact that the fixing elements are not disposed equidistantly, but with variable spacing in the two directional dimensions of the wire lattice. This is fundamentally impossible with the previously known stamping of a wire lattice out of a prefabricated broad mesh grid. However, it is also possible to associate each intermediary piece of the flow rectifier exactly with a wire section of the wire lattice, which is disposed offset in the flow direction parallel to the associated intermediary piece with a high degree of precision that is predetermined by means of the fixing elements.
It is advantageous to warm-caulk the wires of the wire lattice to the tube since this only requires a low manufacturing cost.